In U.S. Pat. No. 4,642,733 is disclosed a "plug in" protective device, for installation within loadcenters, for the dissipation of line surges and the like. The device comprises a "plug in" surge protector of physical width and mounting means compatible with those of conventional "plug in" circuit breakers.
Such "plug in" surge protectors need not be "paired" but may be individually mounted within an operating loadcenter, wherever "stab mounting space" is available, at least one protecting the circuits on at least one bus.
Adding "plug in" surge protective devices, particularly in loadcenters already installed and in use, reduces the "stab spaces" available for circuit breakers. An alternate embodiment comprising a breaker combined with a surgeprotector, both connected in parallel to a "stab" on the load center bus, or having a common bus contact within the combination breaker/protector, is thus both desirable and frequently necessary.
The problem of limited or unavailable "stab spaces" in loadcenters has over the years been addressed by most loadcenter manufacturers, by providing a "thin" breaker, usually one half the thickness of the original "thick" breaker, but having the same current rating. In similar fashion, a "thin" surge protector, having suitable operating characteristics, can be made in the manner of the "thick" one.
"Plug-in thin" breakers of some manufacturers (FIG. 1) may be independent devices, the "stabs" plugged directly into "stabgripper" apertures in the bus.
"Plug-in thin" breakers of other manufactures (FIG. 2) may have a single "bus stab contact" which engages with a "mating stab" formed by lancing and bending the bus metal, or by fastening a "finger" to the bus. The single "bus stab contact" within the unitary breaker enclosure feeds two, or even four, "thin" breakers, and has been factory assembled. One or two of these breakers may be replaced, in this invention, by surge protectors, of similar construction, and having appropriate mounting means.
Study should be given to the "working life" of the conventional breaker compared with that of a MOV type surge protector. If the estimated life of a MOV plug-in element is much less than that of a conventional plug-in breaker, as may be the case in areas with frequent voltage surges, it should be possible to easily separate a defective MOV element from a plug-in breaker which yet has years of useful life, and replace only the defective MOV element.
Such an objective can be achieved for the bus and breaker construction shown in FIG. 2, by making provision for each of the elements to make contact on opposite sides of the load center "stab," and by providing means for quickly exchanging either a defective breaker or surge protector element.